This application is based on application No. 2001-9347 filed with the Korea Patent Office on Feb. 23, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a mask assembly for a cathode ray tube and, more particularly, to a mask assembly for a cathode ray tube which effectively prevents a display screen from manifesting a microphony phenomenon due to vibrations of a tension mask in a tube axis direction.
2. Description of the Related Art
Generally, a cathode ray tube is a display device where electron beams emitted from an electron gun strike phosphors on a phosphor screen to display desired picture images. A shadow mask is provided in the cathode ray tube as a color selection electrode to direct R, G, B electron beams from the electron gun to the corresponding R, G, B phosphors.
In a fabrication process of the shadow mask, a plurality of beam-guide apertures are first formed in a mask body, and then it is drawn. The shadow mask bears an extremely weak strength due to factors such as thinness, a large volume, and a large number of the beam-guide apertures. Hence, a so-called doming phenomenon occurs where the mask is thermally expanded toward the phosphor screen because of continual scanning of the electron beams.
When the shadow mask is deformed or suffers the doming phenomenon, the beam-guide apertures thereon are displaced from their correct positions, and do not perform a beam-guide operation, thereby deteriorating color purity. Therefore, in order to overcome the shortcomings of the conventional shadow mask and cope with screen flattening, a tension mask has been developed. The tension mask is mounted within the tube while bearing a tensional strength. U.S. Pat. No. 3,638,063 incorporated herein by reference, discusses an aperture grill-type tension mask. The mask is fitted to a frame such that strips thereon are spaced apart from each other by a predetermined distance while bearing a unidirectional tension.
In the above-structured shadow mask, the thermal expansion is absorbed by way of tensional strength obtained when mounting the strips. The strips are formed with a thin steel plate bearing a thickness of about 0.1-0.15 mm. The strips are not connected to each other, and only both ends of each strip are fitted to the frame. In this structure, each strip is independently vibrated even with sound impact from a speaker, and induces a display screen to manifest a microphony phenomenon while deteriorating the color purity.
U.S. Pat. No. 4,942,332 incorporated herein by reference, discusses a mask where a plurality of strips are spaced apart from each other while forming slots between them, with real bridges interconnecting the strips. Long sides of the mask are fitted to supporting members. In the mask, the real bridges interconnecting the strips can reduce the microphony phenomenon to some degree.
Furthermore, Japanese Patent Publication Laid-Open No. Hei11-312476, incorporated herein by reference discusses a tension mask fitted to a frame that is arc-shaped with a predetermined curvature corresponding to a shape of a panel. Damper wires with a very small diameter of 10-20 xcexcm are fitted to the tension mask with a predetermined tensional strength. The damper wires contact the mask while proceeding perpendicular to the beam-guide apertures. The damper wires can also reduce the microphony phenomenon to some degree.
However, in the tension mask with damper wires, a non-effective portion at short sides of the mask is rotated toward the panel due to the tensional strength of the damper wires. Consequently, the damper wires do not contact the tension mask in an appropriate manner, so that the damper wires cannot effectively prevent the microphony phenomenon.
The damper wires may have a sufficient strength for controlling the vibration of the strips, but in a case of the tension mask with real bridges and damper wires, as the mask exhibits face vibrations due to the real bridges, the damper wires alone cannot effectively compensate for such face vibrations. Furthermore, a screen bears lines due to the shadowing of the damper wires.
Various objects and advantages of the invention will be set forth in part in the description that follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
It is an object of the present invention to provide a mask assembly for a cathode ray tube that effectively prevents a display screen from suffering a microphony phenomenon due to external impacts.
This and other objects may be achieved by a mask assembly for a cathode ray tube with the following features. The mask assembly includes a shadow mask, a mask frame, and vibration damping members. The shadow mask has a rectangular-shaped effective portion with a plurality of beam-guide holes, and a non-effective portion surrounding the effective portion. The mask frame has a pair of supporting members along long sides of the shadow mask, and a pair of elastic members spacing the supporting members from each other by a predetermined distance. The shadow mask is supported by the mask frame during a tensioned state. The vibration damping members dampen the vibration of the shadow mask in a tube axis direction. The vibration damping members are tensioned in a longitudinal direction such that the vibration damping members pressurize the non-effective portion standing with the long sides of the shadow mask against the mask frame.
The effective portion has a plurality of strips spaced apart from each other by a predetermined distance while forming slots to be used as the beam-guide holes, with real bridges interconnecting neighboring strips, and a plurality of dummy bridges provided within each slot without interconnecting the neighboring strips.
The vibration damping members are a pair of damper strips. Each damper strip has a variable width or thickness in the longitudinal direction, and end portions of each damper strip are fixed to fixtures internally provided at the lateral sides of the supporting members, or directly to the lateral sides of the supporting members. Wedges are partially inserted between the non-effective portion and the damper strips.
Alternatively, the vibration damping members may be a pair of coil springs. In this case, a pressurizing force of each coil spring is distributed by differentiating a diameter of the center of the coil spring from a diameter of an end portion of the coil spring.
These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.